SIRIUS 3RT2 contactors/contactor assemblies
2.4 Configuration
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
135
2.4.10 Starting three-phase motors with reduced starting current peaks (3RA24
contactor assembly for star-delta (wye-delta) start)
Applications
The 3RA24 contactor assembly for star-delta (wye-delta) start is used for starting three-
phase motors where current peaks need to be reduced and a low load torque is required
during startup. With this circuit type, the motor's starting current is reduced by 1/3
(proportional load torque) compared with direct startup.
NOTICE
Increased current peaks
When switching over from star operation to delta operation, the motor may be subjected to
compensation processes (fueled by an unfavorable line frequency/rotor field constellation),
which would result in higher current peaks than would be the case if the stationary motor
were connected directly in the delta circuit.
Please take these current peaks into consideration when configuring a contactor assembly
for star-delta (wye-delta) start. For detailed information, please refer to section "Technical
backg
rou
nd information (Page 136)"
Note
The preferred wiring for the 3RA24 contactor assembly minimizes this effect.
The 3RA24 contactor assemblies for star-delta (wye-delta) start described below have been
dimensioned for standard applications.
Note
Contactor assemblies for star-delta (wye-delta) start for special applications, such as very
heavy starting or star-delta (wye-delta) startup of special motors, must be customized. When
dimensioning combinations for special applications such as these you can obtain support
from Technical Assistance (www.siemens.com/lowvoltage/technical-assistance
).
Versions
The 3RA24 contactor assemblies for star-delta (wye-delta) start are available with a uniform
performance range of 5.5 kW to 22 kW (utilization category AC-3). The 3RA24 contactor
assembly for star-delta (wye-delta) start is 135 mm wide.
The fully wired and tested 3RA24 contactor assemblies consist of three 3RT20 motor
contactors (line contactor, star contactor, and delta contactor), the 3RA2816-0EW20 function
module for star-delta (wye-delta) start which can be plugged on to the contactors (without a
communication connection), and main circuit wiring modules.
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